During the purification of crude TNT with aqueous sodium sulfite, a waste liquor is produced, which contains sodium 5-methyl-2,4- and -2,6-dinitrobenzenesulfonates, of which the major product is sodium 5-methyl-2,4-dinitrobenzenesulfonate. This waste liquor represents a disposal and pollution problem as well as a loss of the aforesaid sulfonates, which ordinarily amount to about 4% of the TNT produced.